Miniaturization of electronic components has led to various improvements in semiconductor technology to make electronic components ever-smaller. Such components may include simple components such as diodes, up to complex components such as integrated circuits. Apart from electronic components, mechanical components can also be manufactured using the same technology.
In the art of semiconductor technology, it is commonly known that a wafer of semiconductor material, typically silicon, is processed to form the components in a surface area of the wafer. The wafer is macroscopic, having a diameter ranging in the order of 20-300 mm, while the components are microscopic, typically having a size in the micrometer range. Each component is made in a small wafer portion, with the various wafer portions being located at a small distance from each other. After the processing steps, the wafer is cut to separate the various wafer portions from each other, so that the components become available independent from each other. After separation, each separated wafer portion is referred to as a die, and the separation process is known as dicing. The present invention relates particularly to the field of dicing.
The various wafer portions are typically arranged in a square pattern, separated by mutually orthogonal lanes, also indicated as “dicing streets”. The separation process involves applying a cut in each dicing street. Evidently, it is desirable that the surface area of the wafer is used as efficiently as possible, therefore said dicing streets are very narrow, which makes the precision requirements for the dicing processing very severe. Further, along the said orthogonal lanes the top layer is an insulating or low-conductivity semiconductor material, which may be relatively brittle, and a traditional blade dicing method will cause severe damage to this top layer.
To overcome these problems, a hybrid dicing process has already been proposed in the prior art. This process is basically a two-step process, including a first step where radiation, typically a high power laser beam, is used to remove the top layer of the dicing streets, and a second step where a blade is used to cut the bulk silicon. The first step is also indicated as “radiative cutting”, or more conveniently as “laser cutting”. The present invention relates more particularly to a method of laser cutting.
FIG. 1 is a schematic top view of a portion of a wafer 1, showing component portions 3 separated by dicing streets 4. FIG. 2 is a schematic cross section of a portion of the wafer 1, illustrating (on an exaggerated scale) subsequent steps in a laser grooving process. The top layer of the wafer 1 is indicated at reference numeral 2. In a first step of the laser grooving process (see FIG. 1 right-hand side, and FIG. 2 second picture), a relatively low power laser beam 11, 12 is directed to an edge area 13, 14 of a dicing street 4. Arrows indicate the relative movement of the laser beam 11, 12 and dicing street 4 with respect to each other, in a direction parallel to the longitudinal direction of the street 4. This relative movement may be practised by holding the wafer stationary and moving the laser beam, or by holding the laser beam and moving the wafer, or both. In practice, it is more convenient to hold the optical system stationary and move the wafer; nevertheless, the movement will be indicated as a “cutting” or “scribing” movement of the laser beam. Laser power and beam speed are controlled such that the top region of the wafer 1 is removed (ablated) up to a relatively low depth and small width; the resulting elongate recesses at opposite sides of the streets 4 are indicated as “trenches” 15, 16. The depth of the trenches 15, 16 is larger than the thickness of the top layer 2. This first step of the laser grooving process is hereinafter referred to as “cutting” or “scribing” trenches.
In a second step of the laser grooving process (see FIG. 1 left-hand side, and FIG. 2 lower picture), a relatively high power laser beam 21 is directed to a central area 17 of the dicing street 4. The width of this laser beam 21 covers the entire street width between the trenches 15, 16. The resulting elongate central recess in the centre of the street 4 is indicated here as a “furrow” 18. This second step of the laser grooving process is hereinafter referred to as “scribing” a furrow.
The combination of furrow 18 with adjacent trenches 15, 16 will be referred to collectively hereinafter as a groove 20. Depending on the precise process parameters, the individual furrow 18 and trenches 15, 16 may or may not be recognizable in the grooves 20. The overall process of forming a groove 20 will also be indicated as “scribing” a groove.
In practice, the high power laser beam 21 may consist of a matrix of high power laser beams 22, which together effect the material ablation up to the desired depth and width. With such matrix, it is simpler to achieve a desired ablation profile, i.e. a relatively wide furrow with substantially constant depth over a large central part thereof.